1. Technical Field
The present invention relates to a support system for anchoring sidewalls of a dual containment vessel and for employing an integral leak detection system. More particularly, it provides for a recessed foundation arrangement for securely supporting a primary tank sidewall above a secondary tank floor member, allowing said floor to be a continuous membrane. This arrangement advantageously decreases the susceptibility of the primary tank to overturning when subject to seismic activity, yet maintains the integrity of the dual containment vessel system. In addition, the present invention provides a means for the monitoring o fluids that have breached the primary and/or secondary containment tanks.
2. Background Art
The construction and use of containment vessels having a dual wall type of construction is well known. These structures are commonly known as a tank-within-a-tank, although other manifestations exist. Vessels or tanks of this nature are typically used for storage of environmentally hazardous materials, especially fluids, because the second surrounding tank contains any fluid leaking from the primary tank and protects the surrounding environment from the same. The construction and use of containment vessels or tanks having a continuous recessed base foundation support system is also well known. Such systems are better able to withstand external forces such as wind and seismic activity.
In furtherance of the goal to provide a leak-proof containment vessel, inventions have been proposed to meet this challenge. The predominant solution has employed multiple containment structures, usually comprising a primary tank enclosed by a secondary tank. In this manner, should a breach occur in the primary tank, any liquid escaping therefrom would be retained by the secondary tank. A collateral benefit is that the secondary tank often provides a means to shield the primary tank from undesirable attacks (e.g. corrosion, impact, etc.).
Because such dual containment structures usually contain environmentally hazardous fluids, detection of a breach of the primary tank is essential. To this end, inventions have been proposed to monitor the secondary containment tank for the presence of the liquid contained in the primary tank. Should liquid be detected in the secondary tank, steps then could be taken to evacuate and repair the primary tank. In this manner, integrity of the system and safety of the environment could be maintained.
However, efficient detection of a breach in the secondary containment tank has not been previously addressed. For example, should a breach occur in the primary tank and the secondary tank also has become defective or violated, a means to detect a secondary tank leak becomes essential to ensure the continued safety of the surrounding environment.
When designing large dual containment vessels, the ability of that structure to withstand external forces is an important design factor. Because the primary tank has primary responsibility for containing the liquid and is subject to the greatest stress, it is of particular importance to design the anchoring method of that tank such that it will not buckle or break during external influences such as seismic activity in addition to withstanding internal forces encountered during normal use. As the height of a dual containment vessel increases the internal hydrostatic pressures and overturning movement due to external forces naturally increase. Therefore, the anchoring system used must be adequate to ensure the integrity of the vessel. Presently, anchoring systems are used that typically include piercing or severing a floor member of a secondary tank in a dual tank system. Such methods impinge on the structural soundness of the secondary tank, thereby decreasing its effectiveness should a breach occur in the primary tank. A need therefore exists to provide a dual containment vessel that has a superior resistance to external forces such as seismic activity and that does not decrease the integrity of the secondary tank.
Single containment vessels have identified and dealt with these factors. Very early designs of single containment vessels relied on the weight of the structure to keep it secure and immobile. Subsequent designs incorporated anchoring the structure using external attachments primarily comprising "L" brackets attached to the vessel and a foundation. While these newer designs were an improvement, they did not provide total structural integrity--shearing forces would cause the anchors to fail. The most recent incarnation involves a subterranean foundation system. This system comprises an annular trough roughly the diameter of the vessel walls into which wall footings are placed, much like the foundations formed for buildings or residential housings. This recessed foundation system advantageously provides for an increased resistance to undesirable external forces and a secure means for anchoring the vessel.
While this system provides a means for soundly supporting and anchoring single containment vessels, this technique has not been utilized in the construction and use of dual containment vessels. Consequently, such a foundation system lacks the ability to contain liquid escaping from the vessel and the ability to monitor for such conditions. Alternatively, dual containment vessels do provide this leak protection, but heretofore lack the structural integrity inherent in the recessed foundation system employed by the single containment vessels. Therefore a need clearly exists to have a containment vessel system that could employ the advantages of a foundational support system employed by the single containment system with the leak prevention and detection means found in a dual containment system. Heretofore, this need has not been met.